https://leetcode.cn/problems/missing-number-lcci/description/


int missingNumber(int* nums, int numsSize) {
    int a = 0;
    for (int i = 0;i <= numsSize;i++)
    {
        a ^= i;
    }
    for (int i = 0;i < numsSize;i++)
    {
        a ^= nums[i];
    }
    return a;
}